1. Field of the Invention
The present invention relates to line light sources and optical fibers. More particularly, the present invention relates to an optical fiber that couples light from the side of the fiber.
2. Discussion of the Background
Various applications utilize line light sources. A line light source can be from a few centimeters to a few meters long, or even longer. Line light sources are used in optical inspection operations that utilize high throughput and therefore, a large, long area of inspection that examines items flowing through this area. Important criteria of line light sources include that they must be uniform, efficient, low cost, reliable, and with minimal extraneous heat generation. Another important criteria in some systems utilizing line light sources is that the line source be highly directional so that all of the light impinges on only one small area. An additional criteria is that the line light source has only certain spectral components.
Current line light sources include arrays of diodes, long halogen lamps, and scattering fibers. One solution uses fibers with tilted gratings imprinted in the fibers. However, this fiber grating solution requires a non-uniform grating strength to arrive at the proper scattered light uniformity since the light is depleted as the light propagates through the grating. Moreover, the grating can couple out only one polarization, making the light sources less efficient. Also, if there is sufficient birefringence along the fiber, the polarization can rotate along the fiber, making the out-coupled power of the light non-uniform. Furthermore, any polarization fluctuations can result in instability of the out-coupled power. Finally, if a narrow band spectrum is required, this must be supplied at the fiber input, and such laser sources can be expensive and inefficient.